EFFISAYIL® 1 was a randomized, placebo-controlled study of spesolimab, an anti-IL-36 receptor antibody, in patients presenting with a generalized pustular psoriasis (GPP) flare. Treatment with spesolimab led to more rapid pustular and skin clearance versus placebo in approximately half of the patients. Here we present histologic, transcriptomic, and proteomic analyses of lesional and non-lesional skin, and whole-blood samples collected from EFFISAYIL® 1. Treatment with spesolimab led to a transition toward a non-lesional profile, with a downregulation of gene expression in the skin of IL-36 transcripts (IL-36α, IL-36β, IL-36γ) and those associated with neutrophil recruitment (CXCL1, CXCL6, CXCL8), proinflammatory cytokines (IL-6, IL-19, IL-20), and skin inflammation (DEFB4A, S100A7, S100A8). Changes were manifest at Week 1 and sustained to Week 8. At the systemic level, reductions in serum biomarkers of inflammation (IL-17, IL-8, IL-6) were sustained until 12 weeks post-spesolimab treatment. Considerable overlap was observed in the spesolimab-induced changes in gene and protein expression from skin and blood samples, demonstrating the molecular basis of the effects of spesolimab on controlling local and systemic inflammation. Data are consistent with the mode of action of spesolimab, whereby inhibition of the IL-36 pathway leads to subsequent reductions in the key local and systemic pathologic events associated with acute GPP flares.